Contamination control



Nov. l, 1949.

J.v ROTHSTEIN CONTAMINATION CONTROL Filed May 10, 1946 FIC. 2

-|s FIG. 3

IN VEN TUR.

JEROME ROTHSTEIN ATTORNEY Patented Nov. 1, 1949 UNITED STATES PT NT OFFICE 3 Claims.

(Granted under the act of March 3, 1883, as

amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to a means whereby grid contamination in a thermionic tube may be annulled.

One of the objects of this invention is to pro- Vide an arrangement whereby the detrimental eiect of barium carried over from the oxide cathode to the grid is substantially completely avoided.

Another object is to provide a grid structure, which, because of its large surface area, will lessen the concentration of contaminant on the outer surface.

Still another object is to provide a grid structure in which a getter for the contaminant is incorporated in the grid structure.

These and other objects will become apparent in the specification and in the accompanying drawing in which:

Figure l shows a grid wire constructed of a plurality of strands;

Fig. 2 shows the cross section of a grid wire 'of sintered construction;

Figure 3 is a cross section of grid wire composed of an alloy whose surface characteristics have been changed through leaching.

The efliciency in a power oscillator having an oxide cathode drops rapidly when the grid becomes contaminated with barium, resulting in thermionic emission at the grid.

While suitable grid treatments have been developed for ameliorating thorium contamination none have so far been produced which are effective against barium contamination.

The present invention provides a construction suitable to prevent barium contamination thereby making available for use in transmitter tubes, etc., the comparatively eiiicient barium oxide cathodes.

In attaining these objects, I propose to construct a grid not out of a solid wire or sheet as heretofore but in accordance with a construction which will provide a large internal surface and which will include in addition a getter for barium.

As shown in Figure 1, one embodiment of my invention pertains to a grid wire I constructed of a large number of relatively fine strands II and I2, so as to provide a large internal surface. Wires I I at the outside of the strand could be made of nickel, tungsten, tantalum, or the like while the inner wires I2 are made preferably of gold or of a gold rich palladium-gold alloy, platinum, palladium, or other metal which alloys with barium.

The first advantage thereby derived in the arrangement of` Figure 1 is that the barium tends to migrate over the grid surface, and since, for this grid, a much larger area is provided over which the contaminant may spread, it is obvious that the concentration of barium on the outer surface of the grid wire is much less than in the case of a solid wire. As an eX- ample, if an ordinary grid calls for 12 mil wire my construction may utilize 144 strands of one mil wire to obtain the same cross section with the desirable result, however, that the outer surface would be less than 10% of the internal surface. The internal contamination will not give rise to harmful emission due to the shielding provided by the strands, and in addition the effect of space charge will reduce the current to a negligible value.

It is clear that if the internal surface is very much larger than the outer surface more of the barium or thorium will be on the inside leaving the outer or emitting surface relatively uncontaminated. It follows therefore that efficiency will not drop off appreciably until the whole grid is saturated.

The second advantage to the construction provided in Figure 1 is that resulting from the incorporation of strands I2 of gold or palladiumgold alloy or other metals which metals have the property ofalloying further with barium. Thus, not only is the contaminant dispersed very thinly over the outer surfaces of wires I I but there is a constant action of alloying or cleaning up of the contaminant due to the wires I 2, thereby further reducing the contamination level.

Figure 2 shows another modification in which a grid wire I3 is constructed with an outer layer i4 of metal sintered in the form of a wire, with a strand I2 of palladium gold alloy or other similar metals incorporated at its center. This construction is readily produced in accordance with well known powder metallurgy techniques and is quite porous and has inherently a large number of microscopic spaces resulting in a very large inner surface. As in the case of the wire in Figure 1 the sintered wire of Figure 2 would likewise provide a large internal surface over which the barium could disperse and eventually alloy with the gold or palladium gold alloy at the center.

In the modification of Figure 3 a wire I5 is drawn from a platinum-gold alloy or similar 3 metal and is leached with potassium cyanide or its equivalent to provide a relatively gold free outer area I6 and a relatively gold rich central portion Il. In this embodiment, porous portion IE provides a large surface While the central portion Il acts as a getter for the barium exactly as do Wires I2 in the modications of Figures 1 and 2. Alloys other than platinum-gold may be utilized with other leaching agents to produce equivalent results.

While I have shown only three modifications it Will be obvious to those skilled in the art that other shapes and arrangements e. g. perforated sheets for thyratron control electrode are possible Within the scope and extent of my invention.

I claim:

1. Material for making grids for electron tubes, comprising an outer electrically conductive portion in continuous contact with an electrically conductive inner getter portion enclosed by the cuter portion, said inner and outer portions each consisting of a plurality of Wires, the exposed exterior 'surface displayed by said outer portion being only a small fraction of the total `surface displayed by both inner and outer portions.

2. Material for making grids for electron tubes, comprising an outer electrically conductive por- 4 tion in continuous contact with an electrically conductive inner getter portion enclosed by the outer portion, said outer portion being microscopically porous.

3. Material for making grids for electron tubes, comprising an outer electrically conductive por- Jdon in continuous Contact With an electrically conductive inner getter portion enclosed by the outer portion, said inner portion containing at least one of the metals selected from the class consisting of gold, platinum and palladium.

JEROME ROTHSTEIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,286,089 Pfanstiehl Nov. 26, 1918 1,689,030 Holland Oct. 23, 1928 1,712,370 White May 7, 1929 1,871,363 Fritz Aug. 9, 1932 1,949,849 Van Gessel et al. Mar. 6, 1934 1,989,954 vVan Gessel Feb. 5, 1935 2,175,345 Gadies et al Oct. 10, 1939 2,275,864 Record Mar. 10, 1942 

